What is in this article?:
The compliance of compressed air has kept it from gaining widespread use in motion bases for ride simulators and virtual reality (VR) attractions. But at least one company has turned a liability into an asset by developing a pneumatically powered motion base that offers impressive performance without an exorbitant price.
As a commercial airline pilot for 20 years, I often underwent training and testing in flight simulators. I was always intrigued by these machines and wanted to build my own scaled-down version. Learning how complex and tremendously expensive these machines are offered no encouragement. Still, I felt convinced that attacking the problem by trying fresh ideas without a bunch of self-imposed restrictions, and learning from experience, would lead to a solution.
Retiring as a commercial pilot allowed me to devote the time and effort to transform my collection of ideas into a physical reality. Upon developing my first motion base, I was, of course, eager to show it off. This motion base was a chair mounted on a platform articulated by six cylinders and controlled by a joystick. Pivoting the joystick in a certain direction caused the chair take off in that direction.
My engineer friends thought the chair was uncontrollable. In their view, it had a mind of its own, but that’s what I wanted — it seemed alive. When we discussed details of the design, they wanted to see huge, complicated equations and horrendous algorithms that took everything into account. They were used to designing stiff systems for industry, with all variables tightly controlled. Naturally, they were disturbed that I ran the motion base with compressed air, because its compliance, or sponginess, does not lend itself to a stiff motion control system. The big difference between my perception and that of convention is that compliance is a power to be used rather than restricted.
To demonstrate compliance, if the motion base is powered, but no signal is provided by the joystick, the motion platform assumes a level position. If you suddenly jump onto one corner of the platform and hold on, the platform will dip, but then right itself. When you jump off, that corner rises, but the platform again quickly rights itself back to its level, equilibrium state. This is what makes the motion base seem alive. In contrast, jumping onto a stiff hydraulic or mechanical motion base would have little or no effect on the position of the motion platform.
Subsequent modifications and improvements eventually led to what is now the Cyber Air Base, Figure 1. Currently, the Cyber Air Base produces 6-axis motion in conjunction with a number of audio-visual programs for simulation and virtual reality (VR) entertainment. VR is the next step beyond simulation. In simulation, you are a passenger in a predetermined journey. It’s fun and exciting, but in VR, you become the pilot or driver, not just a passenger. You control where you want to go, when, and how, so no two experiences are ever exactly the same — and they are usually unpredictable, which fits perfectly the character of the Cyber Air Base.
Vitrtual reality as an application
The reason motion bases for simulation and virtual reality attractions have been so complicated and expensive is because they have been engineered using the same technology as that applied to industrial equipment. Industrial machines need stiff systems for precise control and impeccable repeatability. Because everything is always changing in a virtual reality environment, repeatability is not as important as it is in an industrial application.
In a manufacturing environment, you want variables to be controlled and predictable. But this is a motion base for a virtual reality experience. Unlike a ride simulator, virtual reality doesn’t follow a script or repeat the same sequence of events in a program time after time. Each encounter is unique, and the person involved has nothing to compare it to except previous encounters. But that doesn’t necessarily mean he or she should expect events to occur the same way in a new encounter as they did before.
For example, if the virtual reality experience places you in the driver’s seat of a vehicle, the motion base may be oriented in a certain attitude when your virtual vehicle is at a specific location. If you move the vehicle away from that location and return to it later, the motion base does not necessarily have to be oriented exactly the same way as it was before. You probably wouldn’t have noticed or remember precisely how you were oriented at a specific location. More importantly, virtual conditions may have changed since you were at that location last time, so maybe you shouldn’t even be at the same orientation.
Not only are VR motion bases a little more forgiving of repeatability than industrial machines are, but virtual reality also does not require the tightly controlled acceleration and deceleration of industrial motion control systems. Virtual reality motion bases need only match motions that can be sensed by humans. If you have good visual effects, the human imagination fills in much of the rest, so your motion base only has to approximate the movements implied by the visual program.
A major challenge for virtual reality systems has been getting a motion base to respond in real time. We’ve been able to maintain real-time response while continually increasing the sophistication of the visual portion of a virtual reality presentation as computers become faster, more powerful, and as we develop ways of manipulating software more effectively. The dynamics of conventional motion base control has not increased at the same rate, however. Because the physical characteristics and their dynamics are unique to each application, each new application has to start almost from scratch.
This is important, because we don’t have the luxury of using the majority of our computer power for motion control. We need it for VR graphics that are becoming more three-dimensional looking and with greater detail. We can’t compromise graphics for motion control. On the other hand, we need motion to occur in real time, because we don’t want to slow down graphics just so the motion can keep up. The need to use the computer for graphics rather than motion control is becoming increasingly important as motion bases begin interacting with each other. Virtual reality is no longer an individual experiencing his or her own solo encounter in an individual motion base. We are working toward six motion bases all in the same VR environment simultaneously. Whatever one person does in his or her motion base affects what the five other individuals experience.